We investigate the degree of price competition among telecommunication firms. Underlying a Bertrand model of price competition, we empirically model pricing behaviour in an oligopoly. We analyse panel data of individual pricing information of mobile phone contracts offered between 2011 and 2017. We provide empirical evidence that price differences as well as reputational effects serve as a signal to buyers and significantly affect market demand. Additionally, we find that brands lead to an increase in demand and thus are able to generate spillover effects even after price increase.

We explore how competition between physicians affects medical service provision. Previous research has shown that, without competition, physicians deviate from patient‐optimal treatment under payment systems like capitation and fee‐for‐service. Although competition might reduce these distortions, physicians usually interact with each other repeatedly over time and only a fraction of patients switches providers at all. Both patterns might prevent competition to work in the desired direction. To analyze the behavioral effects of competition, we develop a theoretical benchmark that is then tested in a controlled laboratory experiment. Experimental conditions vary physician payment and patient characteristics. Real patients benefit from provision decisions made in the experiment. Our results reveal that, in line with the theoretical prediction, introducing competition can reduce overprovision and underprovision, respectively. The observed effects depend on patient characteristics and the payment system, though. Tacit collusion is observed and particularly pronounced with fee‐for‐service payment, but it appears to be less frequent than in related experimental research on price competition.

We present a game-theoretic model of the repression–dissent nexus, focusing on preemptive repression. A small group of instigating dissidents triggers a protest if each dissident participates. The dissidents face random checks by security forces, and when an individual dissident is caught while preparing to participate, he or she is prevented from doing so. Each dissident can invest in countermeasures, which make checks ineffective. For large benefits of protest, higher preemptive repression in the form of a higher number of checks has a deterrence effect and makes dissidents less prone to invest in countermeasures, decreasing the probability of protest. For small benefits of protest, higher preemptive repression instead has a backfiring effect. Both myopic and farsighted governments avoid the backfiring effect by setting low levels of preemptive repression (velvet-glove strategy). However, only a farsighted government is able to exploit the deterrence effect by maintaining a high level of preemptive repression (iron-fist strategy).

2016

We study a game between a network designer, who uses costly links to connect nodes in a network, and a network disruptor who tries to disrupt the resulting network as much as possible by deleting either nodes or links. For low linking costs networks with all nodes in symmetric positions are a best response of the designer under both link deletion and node deletion. For high linking costs the designer builds a star network under link deletion, but for node deletion excludes some nodes from the network to build a smaller but stronger network. For intermediate linking costs the designer again builds a symmetric network under node deletion but a star‐like network with weak spots under link deletion.

We construct two-player two-strategy game-theoretic models of by-product mutualism, where our focus lies on the way in which the probability of cooperation among players is affected by the degree of adversity facing the players. In our first model, cooperation consists of the production of a public good, and adversity is linked to the degree of complementarity of the players׳ efforts in producing the public good. In our second model, cooperation consists of the defense of a public, and/or a private good with by-product benefits, and adversity is measured by the number of random attacks (e.g., by a predator) facing the players. In both of these models, our analysis confirms the existence of the so-called boomerang effect, which states that in a harsh environment, the individual player has few incentives to unilaterally defect in a situation of joint cooperation. Focusing on such an effect in isolation leads to the "common-enemy" hypothesis that a larger degree of adversity increases the probability of cooperation. Yet, we also find that a sucker effect may simultaneously exist, which says that in a harsh environment, the individual player has few incentives to unilaterally cooperate in a situation of joint defection. Looked at in isolation, the sucker effect leads to the competing hypothesis that a larger degree of adversity decreases the probability of cooperation. Our analysis predicts circumstances in which the "common enemy" hypothesis prevails, and circumstances in which the competing hypothesis prevails.

This paper studies welfare consequences of consumer-side market transparency with endogenous entry of firms. Different from most studies, we consider the unique symmetric entry equilibrium, which is in mixed strategies. We identify two effects of market transparency on welfare: a competition effect and a novel market-structure effect. We show, surprisingly, that for almost all demand functions the negative market-structure effect eventually dominates the positive competition effect as the market becomes increasingly transparent. Consumer-side market transparency can therefore be socially excessive even without collusion. The only exception among commonly used demand functions is the set of constant demand functions.

How is collective defence by players affected when they face a threat from an intelligent attacker rather than a natural threat? This paper analyses this question using a game-theoretic model. Facing an intelligent attacker has an effect if players move first and visibly set their defence strategies, thereby exposing any players who do not defend, and if the attacker is, moreover, not able to commit to a random attack. Depending on the parameters of the game, the presence of an intelligent attacker either increases the probability that players jointly defend (where such joint defence either does or does not constitute a utilitarian optimum), or decreases the probability that players jointly defend (even though joint defence is a utilitarian optimum).

Publications - Working Papers, Reports, Monographys

2018

This note deals with agreeability in nontransferable utility (NTU) differential games. We introduce state feedback Pareto weights to enrich the set of efficient cooperative solutions. The framework is particularly useful if constant weights fail to support agreeability, but cooperation is desired nonetheless. The concept is applied to an adverting differential game.

We show that the Boston school choice mechanism (BM), the student proposing deferred acceptance algorithm (DA) and the top trading cycles algorithm (TTC) generate the same outcome when the colleges’ priorities are modified according to students’ preferences in a “first preferences first” manner. This outcome coincides with the BM outcome under original priorities. As a result, the DA and TTC mechanism that are non-manipulable under original priorities become vulnerable to strategic behavior.

2017

We experimentally study the emergence of networks under a known external threat. To be more specific, we deal with the question if subjects in the role of a strategic Designer are able to form safe and efficient networks while facing a strategic Adversary who is going to attack their networks. This investigation relates theoretical predictions by Dziubinski and Goyal (2013) to actual observed behaviour. Varying the costs for protecting nodes, we designed and tested two treatments with different predictions for the equilibrium network. Furthermore, the influence of the subjects' farsightedness on their decision-making process was elicited and analysed. We find that while subjects are able to build safe networks in both treatments, equilibrium networks are only built in one of the two treatments. In the other treatment, predominantly safe networks are built but they are not efficient. Additionally, we find that farsightedness --as measured in our experiment - has no influence on whether subjects are able to build safe or efficient networks.

In Internet transactions, customers and service providers often interact once and anonymously. To prevent deceptive behavior a reputation system is particularly important to reduce information asymmetries about the quality of the o?ered product or service. In this study we examine the e?ectiveness of a reputation system to reduce information asymmetries when customers may make mistakes in judging the provided service quality. In our model, a service provider makes strategic quality choices and short-lived customers are asked to evaluate the observed quality by providing ratings to a reputation system. The customer is not able to always evaluate the service quality correctly and possibly submits an erroneous rating according to a prede?ned probability. Considering reputation pro?les of the last three sales, within the theoretical model we derive that the service provider’s dichotomous quality decisions are independent of the reputation pro?le and depend only on the probabilities of receiving positive and negative ratings when providing low or high quality. Thus, a service provider optimally either maintains a good reputation or completely refrains from any reputation building process. However, when mapping our theoretical model to an experimental design we ?nd that a signi?cant share of subjects in the role of the service provider deviates from optimal behavior and chooses actions which are conditional on the current reputation pro?le. With respect to these individual quality choices we see that subjects use milking strategies which means that they exploit a good reputation. In particular, if the sales price is high, low quality is delivered until the price drops below a certain threshold, and then high quality is chosen until the price increases again.

2016

On an intermediate goods market we consider vertical and horizontal product differentiation and analyze the impact of simultaneous competition for resources and the demand of customers on the market outcome. Asymmetries between intermediaries may arise due to distinct product qualities as well as by reasons of different production technologies. The intermediaries compete on the output market by choosing production quantities sequentially and for the supplies of a monopolistic input supplier on the input market. It turns out that there exist differences in product quality and productivities such that an intermediary being the Stackelberg leader has no incentive to procure inputs, whereas in the role of the Stackelberg follower will participate in the market. Moreover, we find that given an intermediary is more competitive, his equilibrium output quantity is higher when being the leader than when being the follower. Interestingly, if the intermediary is less competitive and goods are complements, there may exist asymmetries such that an intermediary being in the position of the Stackelberg follower offers higher output quantities in equilibrium than when being in the position of the Stackelberg leader.

Video games are high-involvement products with multiplatform and multiplayer characteristics, which aim to enhance consumer utility by providing opportunities for ‘playful consumption’. However, relatively little research has previously been undertaken into preferences for playful consumption, particularly in the context of multiplayer video games. This study addresses this deficiency in the literature through the analysis of data from a popular online game that includes historic behavioral data for 7 million consumers participating in 868,000 unique game rounds. Our analysis of these data identify the behavioral preferences of consumers in order to identify the factors associated with variations in consumer participation and engagement. We show that consumers value opportunities for score enhancement, with a preference for combat rather than non-combat actions. However, our findings also suggest that consumers value variety and heterogeneity as part of the experience, suffering disutility from factors such as the absence of particular player-roles or vehicle use within a given round. Our results represent the first such evidence on ‘in-game’ consumer preferences and the optimization of the video gaming experience, which has important implications for player matching, utility and willingness to pay for additional content.

We study the willingness to compete in a cognitive task among an entire cohort
of fresh man business and economics students. Combining data from a lab-in-thefield
experiment with university admissions data, we trace the gender gap in
competitiveness at different levels of high school performance. Our results confirm
that, on average, men choose to compete more often. The gender gap disappears,
however, among students with above average high school performance. Female high
school top performers are equally competitive as their male counterparts. In fact,
the overall gender gap is entirely driven by the group of female high school underperformers
who shied away from competition, even when they performed well in our
task. Overall, our findings suggest that high school grades are more than just a
signal of cognitive abilities, because they seem to influence the receivers selfperception
of his or her performance in a competitive environment involved in later
on in life.

2015

We analyze the stability of networks when two intermediaries strategically form costly links to customers. We interpret these links as customer relationships that enable trade to sell a product. Equilibrium prices and equilibrium quantities on the output as well as on the input market are determined endogenously for a given network of customer relationships. We investigate in how far the substitutability of the intermediaries' products and the costs of link formation influence the intermediaries' equilibrium profits and thus have an impact on the incentives to strategically form relationships to customers. For networks with three customers we characterize locally stable networks, in particular existence is guaranteed for any degree of substitutability. Moreover for the special cases of perfect complements, independent products and perfect substitutes, local stability coincides with the stronger concept of Nash stability. Additionally, for networks with n customers we analyze stability regions for selected networks and determine their limits when n goes to infinity. It turns out that the shape of the stability regions for those networks does not significantly change compared to a setting with a small number of customers.

Social psychology studies the "common enemy effect", the phenomenon that members of a group work together when they face an opponent, although they otherwise have little in common. An interesting scenario is the formation of an information network where group members individually sponsor costly links. Suppose that ceteris paribus, an outsider appears who aims to disrupt the information flow within the network by deleting some of the links. The question is how the group responds to this common enemy. We address this question for the homogeneous connections model of strategic network formation, with two-way flow of information and without information decay. For sufficiently low linkage costs, the external threat can lead to a more connected network, a positive common enemy effect. For very high but not prohibitively high linkage costs, the equilibrium network can be minimally connected and efficient in the absence of the external threat whereas it is always empty and inefficient in the presence of the external threat, a negative common enemy effect.

In internet transactions where customers and service providers often interact once and anonymously, a reputation system is particularly important to reduce information asymmetries about product quality. In this study we experimentally examine the impact of the customers' evaluation abilities on strategic quality choices of a service provider. Our study is motivated by a simple theoretical model where short-lived customers are asked to evaluate the observed quality of the service provider's product by providing ratings to a reputation system. A reputation profile informs about the ratings of the last three sales. This profile gives new customers an indicator for the quality they have to expect and determines the sales price of the product. From the theoretical model we derive that the service provider's dichotomous quality decisions are independent of the reputation profile and depend only on the probabilities of receiving positive and negative ratings when providing low or high quality. However, when mapping our theoretical model to an experimental design we find that subjects in the role of the service provider deviate from optimal behavior and choose actions which are conditional on the current reputation profile. In addition, increasing the probability of a negative rating and decreasing the probability of a positive rating both do not affect strategic quality choices.

In this paper, we analyze a model in which two divisions negotiate over an intrarm transfer price for an intermediate product. Formally, we consider bargaining problems under incomplete information, since the upstream division's (seller's) costs and downstream division's (buyer's) revenues are supposed to be private information. Assuming two possible types for buyer and seller each, we rst establish that the bargaining problem is regular, regardless whether incentive and/or eciency constraints are imposed. This allows us to apply the generalized Nash bargaining solution to determine transfer payments and transfer probabilities. Furthermore, we derive general properties of this solution for the transfer pricing problem and compare the model developed here with the existing literature for negotiated transfer pricing under incomplete information. In particular, we focus on the models presented in Wagenhofer (1994).

2012

The phenomenon that groups or people work together when they face an opponent,
although they have little in common otherwise, has been termed the "common enemy
effect". We study a model of network formation, where players can use links to build
a network, knowing that they are facing a common enemy who can disrupt the links
within the network, and whose goal it is to minimize the sum of the benefits of the
network. We find that introducing a common enemy can lead to the formation of
stable and efficient networks as well as fragmented networks and the empty network.